To perform input operations, such as sound volume adjustment or music air selection, on small-sized mobile electronic equipment, an operation is needed for a user to take out the equipment out of a pocket of his/her apparel or from a baggage enclosing it. In Patent Document 1, there is disclosed, as a technique which evades this operation, a mobile phone device in which part of the functions of the mobile phone is separately performed by a device fitted on a user's arm.
In Patent Document 2, there is disclosed a phone device which is attached to a user's ear to allow communication over the mobile phone to be performed based on a trigger signal produced when the user emits a chewing or biting sound.
In Patent Document 3, there is further disclosed an input device that is constructed like a wrist-watch and that inputs user's gestures such as ‘grabbing’, ‘releasing’, ‘twisting’ or ‘shaking’ as command inputs.